A central vehicle door-lock system of the type described in commonly owned patent applications Ser. Nos. 132,977 and 132,978 both filed Mar. 24, 1980 has several door latches each including a detent movable between a locked position securing the door when closed and an unlocked position allowing the door to be opened by means of a mechanism inside the door latch. Each of these latches is associated with a servoactuator having an actuator that is engageable via this mechanism with the respective detent that is in turn moved by an operator. This operator, therefore, can move the actuator and with it the latch detent between a locked and unlocked position and the operator itself is movable by a servomotor into an antitheft position. A lock pawl on this actuator can, in the locked position of the actuator and the antitheft position of the operator, move from a freeing position permitting displacement of the actuator from the locked to the unlocked position and into a blocking position preventing such displacement to lock up the entire latch. The servomotors are all controlled by a central switch which can operate them all jointly between the locked, unlocked, and antitheft positions. Thus when the switch is in the antitheft position the mechanism of the latches cannot displace the detent into the respective unlocked positions.
Such an arrangement has been found to be an extremely good security precaution, as it not only allows all of the door latches to be locked from a single location, but it allows them to be locked in such a manner that even a person having a key or access to the unlock button of one of the door latches cannot open this latch. The latches can only be moved into the unlocked position when the mechanism has been displaced out of the antitheft position.
To this end it has been normal practice simply to provide a separate three-position switch that controls these functions. The key to this switch has normally remained independent of the regular door-latch keys. Thus it is possible for the owner of a vehicle thus equipped to leave the ignition and door key with another, and yet know that only he himself has the key capable of operating the antitheft mechanism so that if the door-ignition key falls into the wrong hands the owner can still lock up the vehicle.
In order to avoid the necessity of having an extra key, a double-duty lock has been suggested for operation of the driver's door lock. Thus the driver can, simply by operating his own door lock with a special key, lock all of the door latches and displace their mechanisms into the antitheft positions.
This double-duty lock is, however, relatively complex. It is normally necessary to provide two separate sets of tumblers in a two-part core. The outer, central part of the core has one set of tumblers which engage in a sleeve formed on the inner core part and carries the other set of tumblers. The standard door and ignition key can operate the outer core part and displace same between the locked and unlocked positions. Only a special key, however, can reach all the way into the inner core part and actuate its tumblers to displace the lock into the antitheft position.
Such a system is advantageous in that the operator of the vehicle can retain the key that operates the antitheft mechanism and, if necessary give out other keys that operate the other systems. Nonetheless, such lock assemblies have proven extremely complex. They must be made carefully, as any failure to stay within very close tolerance will normally have a cumulative effect so that the lock will not operate. What is more, such a lock is relatively long so that mounting it in the motor-vehicle door becomes a problem, in particular when window mechanism must be allowed for. The cost of making such a lock is also relatively high, and the key must normally be a special extra-long key. Finally all of the other door locks in the car must be so constructed that they can accept this extra-long key, again raising the cost of the system incorporating such a lock.